(19) |
 |
|
(11) |
EP 0 780 695 A3 |
(12) |
EUROPEAN PATENT APPLICATION |
(88) |
Date of publication A3: |
|
21.01.1998 Bulletin 1998/04 |
(43) |
Date of publication A2: |
|
25.06.1997 Bulletin 1997/26 |
(22) |
Date of filing: 18.12.1996 |
|
|
(84) |
Designated Contracting States: |
|
DE FR GB |
(30) |
Priority: |
21.12.1995 US 576008
|
(71) |
Applicant: GENRAD, INC. |
|
Concord
Massachusetts 01742 (US) |
|
(72) |
Inventors: |
|
- Pye, Richard
Waltham,
Massachusetts 02154 (US)
- Khazam, Moses
Lexington,
Massachusetts 02173 (US)
|
(74) |
Representative: Waldren, Robin Michael |
|
MARKS & CLERK,
57-60 Lincoln's Inn Fields London WC2A 3LS London WC2A 3LS (GB) |
|
|
|
(54) |
Hybrid scanner for use in a tester |
(57) A hybrid scanner for switching internal analog buses to system pin channels. Semiconductor
switches switch most scanner buses to system pin channels, but mechanical relays perform
switching for at least one bus used for high-current test signals. To perform low-impedance
guarding and/or high-current backdriving, the low impedance, high current bus is typically
connectable to one or more overdriver circuits and a guard voltage potential through
mechanical relays. The scanner is capable of supporting in-circuit tests covering
the most significant regions of the fault spectrum can be made more reliable and much
smaller and less costly than the scanners conventionally used in traditional broad
spectrum testers. It turns out that this test-supporting capability can be achieved
by adding only a few mechanical relays to an otherwise semiconductor-switch-based
scanner. Only those necessary to support low-impedance and high-current test operations.